Chem Phys Research Articles

(Invited) Further Excursions into the Probing of Internal and Interfacial Structure of Ionomer Thin Films

The critical importance of catalyst layer ionomer in numerous transport phenomena (proton conduction, oxygen and water transport) and also in catalyst utilization at multiple length scales is well acknowledged [1]. Thickness-dependent properties such as proton conductivity, water uptake, swelling and water diffusivity have now confirmed that ionomer thin films possess properties significantly different than those of the bulk ionomer materials [2]. Previous work from our group, both independent and collaborative, confirmed suppression of proton conductivity in thin films [3], wettability changes with film thickness and thermal annealing [4], influence of substrate on internal structure [5] and water uptake [6], similarity of T2-relaxations in proton NMR of thin and thick films [7] and recent discovery of temperature-dependent vibrational mode of Nafion ionomer [8]. Tremendous progress made on the topic of ionomer thin films over the past decade has been summarily presented in a recent review [2]. However, many aspects of ionomer thin film structure and properties still remain unknown. For example, despite the confirmation of strong thickness-dependence of ionomer properties for film below 50 nm thickness, one question continues to elude us: what is the critical thickness below which ionic domains cannot be sustained? In a quest to answer this question, we have employed high-resolution electron microscopy to deduce the presence/absence of ionic domains in 4-30nm thin films. There is indication of a critical thickness below which domains are evidently not present. Recent neutron reflectometry measurements from our group have focussed on the quantification of interfacial water (Pt/ionomer interface) and water in the bulk phase of the ionomer thin films on platinum substrate. The results acquired to date indicate that both interfacial and bulk water are dependent on the ionomer molecular structure. Complementing these measurements with GISAXS, ellipsometry, QCM and impedance spectroscopy – a clearer picture of the ionomer structure-property is emerging. The talk will share these new results and discuss the implications of the findings on fuel cell behaviour. Reference: Karan, Current Opin. Electrochem. 5 (1), (2017) 27-35.Kusoglu, A.Z. Weber Chem Rev, 117 (3) (2017), 987-1104K. Paul, R. McCreery, K. Karan, J Electrochem Soc, 161 (14) (2014), F1395-F1402K. Paul, H.K.K. Shim, J.B. Giorgi, K. Karan, J Polym Sci Part B: Polym Phys, 54 (13) (2016), 1267-1277Kusoglu, D. Kushner, D.K. Paul, K. Karan, M.A. Hickner, A.Z. Weber, Adv Funct Mater, 24 (2014), 4763-4774K. Shim, D.K. Paul, K. Karan, Macromolecules, 48 (22) (2015), 8394-8397NE De Almeida, DK Paul, K Karan, GR Goward, J Phys Chem C 119 (3), (2015) 1280-1285VO Kollath, K Karan, Physical Chemistry Chemical Physics 18 (37), (2016) 26144-26150

Multiple Nucleation Processes during the Platinum Electrodeposition Onto Glassy Carbon Electrodes Influence of the Temperature

Introduction The deposition of noble metal particles on some substrates is a field of great interest due the resulting electrocatalytic properties [1, 2]. This is because these particles can exhibit a larger efficient surface area and higher activity [3]. In this sense, Pt nanoparticles deposited on carbon substrates are of special interest [4, 7] due to the low cost, performance and high efficiency. Pt has been electrodeposited onto carbon substrates including highly oriented graphite (HOPG) electrode [6], carbon nanotubes [7], carbon fiber [8], graphite [9], conducting polymers and macroporous carbon [10], glassy carbon [11, 12], among others. In the case of platinum electrodeposition process onto GCE, the information concerning kinetical of the nucleation and growth process is scarce. Therefore, in the present work, we carried out an electrochemical study, in order to understand the Pt electrodeposition process onto this system. Methodology Pt electrodeposits onto GCE were carried out from an aqueous solution containing 0.01 M K2PtCl4 at 25, 30, 35 and 40 oC. All solutions were prepared using analytic grade reagents with ultra pure water (Millipore-Q system) and were deoxygenated by bubbling N2 for 15 minutes before each experiment. A 3-compartment electrochemical cell was used in the electrochemical experiments. An Ag/AgCl and graphite bar served as the reference and counter electrode, respectively. A glassy carbon disk of 3 mm of diameter was used as working electrode and polished to mirror–like finish and ultrasonicated before each experiment. The three electrodes remained connected to an EPSILON potentiostat and a personal computer with the BASi-Epsilon-EC software during the experiments to keep them under control and obtain the results. Results and discussion Figure 1 shows a set of current density transients recorded at a potential value of -0.010 V at different temperature values. These transients were obtained applying an initial potential 0.600 V on the surface of the GCE electrode. In this Figure, it is possible to observe that at shorter times, there is a falling current transient that can be associated with a process that follows Langmuir adsorption-desorption kinetics [13]. After this falling current, in each case, the j-t plots pass through a first maximum (t < 5 s), and a second maximum (t > 5 s), which corresponds to a secundary nucleation and growth process. Also, note that for the transients obtained at 25 y 30 oC, there is a third maximum, which coresponds a new nucleation and growth process. These transients were fitted to a nucleation model which considers that the total current is given by jT=j1+j2+j3, where j1, j2, and j3 corresponds to the nucleation and growth process of the first, second and third maxima, respectively. Conclusions Pt electrodeposition on GCE was studied at different temperatures using potentiostatic and voltammetric techniques. The effect of the temperature effect on kinetics parameters such as diffusion coefficient, and charge transfer coefficient was analyzed. The values of nucleation rate and rate constant of the proton reduction reaction increased with the temperature increment and the applied overpotential. The values of the transfer coefficient was analyzed and a decrease in its value with the temperature increment is observed. Acknowledgements: LHMH gratefully acknowledges financial support from CONACYT (project CB2015-257823) and to the Universidad Autónoma del Estado de Hidalgo. References Spenadel and M. Boudart, J. Phys. Chem., 64 (1960) 204Gunasingbam and C.B. Tan, Analyst, 114 (1989) 695Dong, Q. Qiu, J. Electroanal. Chem., 314 (1991) 223Yin, S., Mu, S., Lv, H., Cheng, N., Pan, M., Fu, Z. Appl. Catal. B Environ. 2010, 93, 233–240He, M. Liu, J.L. Luo, A.R. Sanger, K.T. Chuang, J. Electrochem. Soc. 2002, 149, A808.Lu, G. Zangari, J Phys Chem B. 2005, 109(16), 7998.Zhang, Z. Fang, G.-C. Zhao, X.-W. Wei, Int. J. Electrochem. Sci., 2008, 3, 746.A. Islam, M. S. Islam, Engineering International, 2013, 1(2).Gloaguenb, J.M Légerb, C Lamyb, A Marmanna, U Stimminga, R Vogela. Electrochimica Acta, 1999, 44(11) 1805.Domínguez-Domínguez, S., Arias-Pardilla, J., Berenguer-Murcia, Á. et al. J Appl Electrochem (2008) 38: 259.Dong, Q. Qiu, J. Electroanal. Chem., 1991, 314, 223.-J. Feng, A-Q. Li, A.-J. Wang, Z. Lei, J.-R. Chen. Microchim Acta, 2011, 173, 383.H. Hölzle, U. Retter, and D. M. Kolb, J. Electroanal. Chem., 371, 101, 1994. Figure 1

Design and Activity of Supported Transition Metal Catalysts for Methane to Methanol Oxidation in Electrochemical Fuel Cell

Methane is a relatively inexpensive and abundant resource and its partial transformation to chemicals and chemical fuels presents attractive yet challenging pathways for its utilization. Conventional synthesis for methanol involve a multistep process involving steam reforming of methane with subsequent catalytic reactions, which require high energy input and run at high cost [1]. Alternatively, methane oxidation over catalyst surfaces in an electrochemical cell is a promising single-step approach to achieve a direct conversion of methane to methanol at lower temperatures and low cost [2]. Previous studies have demonstrated that methane can be electrochemically converted into methanol with high selectivity but with low overall conversion efficiency. Increasing the rate of methane conversion can be achieved by systematic improvement of the electrochemical cell design along with the concurrent development of new efficient catalysts materials. Methane oxidation is energetically challenging process and dual role of the catalysts involve first, activation of the relatively inert C-H bond enabling the oxidative hydroxylation, and methanol formation. Second, the effective catalysts should simultaneously inhibit the methanol oxidation, which proceeds with a much lower energy barrier and can result in the formation of formaldehyde, formic acid, carbon monoxide, and carbon dioxide. To date, a variety of the catalysts, among different supported metals (Pd, Ru, Au, Ag) and metal oxides (V2O5, Fe2O3, CoO, Mn2O3, MoO3, CrO), have been tested in electrochemical cell and shown promise for the direct oxidation of methane [2]. However, further systematic studies are essential for understanding the mechanism for methane oxidation, enabling catalysts rational design. On the other hand, bioinspired supported binuclear metal catalysts show potential for high selectivity and conversion [3], but have not yet been explored for electrochemical methane conversion. In this study, first-row transition metal oxides as well as single and binuclear catalysts, supported on well-defined crystalline 2D materials including carbides, oxides, and nitrides will be presented. The catalysts are synthesized with wet-chemical synthesis routes and subsequently fabricated in membrane electrode assembly for testing their activity, methanol selectivity, and conversion efficiency in an electrochemical fuel-cell-type reactor. In-depth structural and chemical analyses of catalysts using a combination of various transmission electron microscopy techniques, complimented with spectroscopy analyses is used to establish structure-property relationship. These insights will provide valuable basis for a scientific-guided approach toward the optimization of the known, and the identification of the new metal oxide and single-site supported catalysts for this challenging process. Ravi, M., et al, Angew. Chemie Int. Ed., 2017, 56, 26464.Tomita, A., et al, Angew. Chemie Int. Ed., 2008, 47, 1462.Starokon, E. V., Phys Chem. C., 2011, 115, 2155.

(Invited) Interactions in Ionomers: From Cations to Confinement

Ion-conductive polymers (ionomers) have been widely used as the solid-electrolyte in energy conversion devices, such as polymer-electrolyte fuel cells (PEFCs) fuel cells, redox flow batteries and water-splitting devices. Ionomers, such as perfluorosulfonic-acid (PFSA), function as the separator-electrolyte in these devices due their high proton conductivity and chemical-mechanical stability.1 In PEFCs, however, ionomers play another key role in Catalyst Layer (CL) structure, where they exist as nanometer-thick electrolyte “thin film" to facilitate transport of ionic and gaseous species to the catalytic particles. As a cathode catalyst film, an ionomer is expected to transport the oxygen molecules to the catalytic sites, which differs dramatically from its gas-separator functionality.2 Once confined to these nanometer thicknesses (< 100 nm), ionomer properties change drastically from the bulk (solid-electrolyte PEM), and are significantly more influenced by its interfaces with the free surface (air) and the catalytic surfaces comprised of carbon and platinum(Pt)-alloyed particles.1,2 In particular, mass-transport limitations in CLs are believed to be related to the transport resistances at the ionomer thin-film, mitigation of which requires a fundamental understanding of ionomer interfaces.3-5 In addition, ionomers, whether as PEMs or in CLs, are exposed to various cations arising from contamination, migration of radical scavengers (such as Cerium), dissolution of catalyst particles (such as Co-alloys), all of which alter the ionomer’s interactions and impact the cell performance.3,6 Thus, throughout this thickness range, it is not only the functionality of ionomer that differs, but also its morphology and transport properties, which are controlled by various interactions. This talk will present an overview of various interactions, from cationic and catalytic particles to dynamic interfaces, and how they influence an ionomer’s intrinsic morphology and transport properties across lengthscales, with a focus on thin films. The latter is in particularly important as the interactions and confinement-driven changes in thin films create an intriguing interplay governing ionomer functionality. We will explore structure-property relationship PFSA ionomers of several chemistries and thicknesses (from micrometer to 10’s of nanometers) in the presence of various types and doping levels of cations to elucidate the underlying origins of governing interactions. Water uptake and swelling behavior as well as nano-morphology of cation-exchanged PFSA membranes and thin films are studied to identify the key factors and interactions impacting their behavior. We will also discuss the role of side-chain chemistry in these interactions, especially in nano-confined thin films. Lastly, I will summarize recent progress in ionomer thin-film research, including improved model systems for thin films that can mimic fuel-cell catalyst structure and environment, and advanced characterization techniques, such as Grazing-Incidence X-ray scattering (GIXS), and how they can be used to probe various interactions. Acknowledgements We acknowledge Adam Z. Weber and Douglas Kushner of Berkeley Lab for helpful discussions, and Michael Yandrasits and Andrew Haug of 3M for helpful discussions and supplying ionomer materials. This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, and was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office, of the office of the Energy Efficiency and Renewable Energy (EERE), of the U. S. Department of Energy (under contract number DE-AC02-05CH11231). References A. Kusoglu and A. Z. Weber, Chem. Rev., 117, 987 (2017).A. Kusoglu, in Encyclopedia of Sustainability Science and Technology, R. A. Meyers Editor, p. 1, Springer New York, New York, NY (2018).A. Kongkanand and M. F. Mathias, J Phys Chem Lett, 7, 1127 (2016).A. Z. Weber and A. Kusoglu, J Mater Chem A, 2, 17207 (2014).M. Tesfaye, A. N. MacDonald, P. J. Dudenas, A. Kusoglu and A. Z. Weber, Electrochem Commun, 87, 86 (2018).A. M. Baker, R. Mukundan, D. Spernjak, E. J. Judge, S. G. Advani, A. K. Prasad and R. L. Borup, J. Electrochem. Soc., 163, F1023 (2016).

Surface Doping Treatment of Octahedral Ptni Alloy Nanoparticle Catalysts for Durable Fuel Cell Cathodes

Proton exchange membrane fuel cells (PEMFCs) convert chemical energy into electricity and uses hydrogen and oxygen as fuel. The sluggish kinetics of the oxygen reduction reaction (ORR) and harsh environment pose challenges on the development of cheap, active and stable catalysts. Shape-controlled bi- or tri-metallic Pt alloy nanoparticles, i.e. octahedral PtNi nanoparticles, have been reported to achieve extremely high mass activity in rotating disk electrode (RDE) experiments and for this reason are considered as a highly promising class of ORR catalysts.1 Despite the high mass activity, the low electrochemical surface area (ECSA), often below 50 m2/g, is considered not optimal for low-loaded PGM cathodes and possible to hinder their performance at higher current density in membrane electrode assemblies (MEA).2 A second challenge is their morphological stability under electrochemical testing. Ni loss and other degradation processes often result in shape changes into more “rounded” or concave structures with loss of the (111) facet and lower activity (Figure 1).3 Introduction of a third metal such as Co, Rh and Mo have been shown to have beneficial effects and is considered a promising step toward shape-stable PtNiX octahedral nanoparticles. In particular, an exceptionally high initial mass activity has been reported for Mo surface doped PtNi catalyst, which also showed good stability in an accelerated test in RDE.4 In this contribution we will show our recent efforts in improving the activity and especially the durability and morphological stability of PtNi based octahedral nanoparticle catalysts. A surface treatment involving the introduction of Mo is applied to octahedral PtNi/C. Activity and stability are evaluated from RDE measurements following a protocol developed inside the INSPIRE project.5 Degradation is monitored by in operando wide angle X-ray scattering (WAXS) performed at European Synchrotron Radiation Facility (ESRF). By this techniques is possible to follow the change in lattice parameter a during different stability tests. The results are correlated to Ni leaching from the crystalline alloy phase. P. Strasser, Science, 2015, 349, 379-380. A. Kongkanand and M. F. Mathias, J Phys Chem Lett, 2016, 7, 1127-1137. L. Gan, C. H. Cui, M. Heggen, F. Dionigi, S. Rudi and P. Strasser, Science, 2014, 346, 1502-1506. X. Q. Huang, Z. P. Zhao, L. Cao, Y. Chen, E. B. Zhu, Z. Y. Lin, M. F. Li, A. M. Yan, A. Zettl, Y. M. Wang, X. F. Duan, T. Mueller and Y. Huang, Science, 2015, 348, 1230-1234. S. Martens, L. Asen, G. Ercolano, F. Dionigi, C. Zalitis, A. Hawkins, A. Martinez Bonastre, L. Seidl, A. C. Knoll, J. Sharman, P. Strasser, D. Jones and O. Schneider, J Power Sources, 2018, submitted. The project leading to this application has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 700127. This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation Programme and Hydrogen Europe and N.ERGHY. Figure 1. Life cycle of an octahedral PtNi nanoparticle showing a degradation pathway to loss of octahedral shape.3 Figure 1

How different are Te clusters—a first-principles study

Density functional theory-based electronic structure calculations are carried out to obtain the geometries corresponding to the lowest three energy values for Tey (y = 2 − 20) clusters. A comparison of the stability from binding energy curve of these clusters with exchange-correlation energy functional approximated within the local density approximation (LDA), generalized gradient approximation (GGA) and hybrid functional (PBE0) indicates the structures to be most stable within the LDA, and these results are also found to be closer to those obtained from the experiments. A transition from two-dimensional to three-dimensional structures is observed at y = 5. Clusters form arm-chair and crown-like structures for small sizes and ring-like geometries for larger sizes. Partial charge density and eigenvalue spectrum reveal that there is no s-p hybridization and the highest occupied states are mostly π non-bonding orbitals. Clusters with even number of atoms show a charge distribution approximately uniformly localized around each atom similar to the σs anti-bonding orbital in Te2. Comparative study of the structural and electronic properties of small Tey clusters (y = 2 − 8), with corresponding isoelectronic sulphur and selenium clusters, predicts sulphur clusters to be most stable and Te clusters to be least stable. Bond lengths increase while bond angles decrease in going from S → Se → Te but the shapes of the geometric structures are more or less the same. Following the work of Ghosh et al. (J Phys Chem C 112:983–989, 2008) on Te helical structures and Pal et al. (Sci Rep 3:2051-1-7, 2013) on Se helical chains, we have carried out spin-polarized electronic structure calculations for helical chains of Tey (y = 3 − 8). Interestingly, we have found that Te helical chains also reveal a behaviour similar to that predicted for Se chains by Pal et al.

Effect of electric wetting on the surface properties of cellulose and chitosan

Cellulose and chitosan have similar structure both with the β(1→4) linked functional groups, e.g., the former linked the D-glucose units and the latter linked D-glucosamine units. Our recent studies have found that these different functional groups have oppositely electric-responses in an electric-assisted capillary rise adsorption process (J Phys Chem B 120: 1121–1125, 2016). This work furthermore reported the electric-wetting behavior of cellulose and chitosan. With the voltage increase, the contact angles between the probe polar solvent and these two biopolymers would be reduced consistently, to lead the surface free energy reduction for cellulose and enhancement for chitosan. This is because that the voltage increase would lead the Lewis acid-base properties reduction for cellulose and enhancement for chitosan. The reason is that the β(1→4) linked D-structures are polar groups with oppositely electric-responses. Therefore, under the electric wetting condition, the polarity of β(1→4)-linked D-glucose would be reduced and the β(1→4)-linked D-glucosamine would be enhanced, respectively.

A Rational Revisiting of Niobium Oxophosphate Catalysts for Carbohydrate Biomass Reactions

Niobium oxophosphate acid catalyst (NbP) has great success in aqueous heterogeneous catalysis, in particular for carbohydrate biomass valorization, thanks to the water-tolerant acid properties of the LA (Lewis) and BA (Bronsted) sites. Attempts to tailor the acid properties of NbP by chemical treatment or dilution in inert matrix to disperse active NbP phase have been recently proposed in the literature (Carniti et al., Appl Catal B 193:93–102, 2016; Aronne et al., J Phys Chem C 121:17378–17389, 2017). The obtained samples have been used with success in the hydrolysis reaction of inulin to fructose and in hydrolysis plus dehydration of cellobiose to HMF. The samples have been further studied with calorimetric acid-titration measurements using 2-phenylethylamine (PEA) basic probe in various liquids (cyclohexane, water, isopropanol, and water-isopropanol mixtures) to study their intrinsic and effective acid strength. A rational revisiting of the surface acid properties of NbP and modified samples, that wants to take into account the acid-sites density and strength and the LAS to BAS ratios measured under different liquid environments in relation with their catalytic activity, is presented.

Nucleation rates of droplets in supersaturated steam and water vapour–carrier gas mixtures between 200 and 450 K

We compare experimental nucleation rates for water vapour in various carrier gases, estimated nucleation rates for steam, and nucleation rates obtained from molecular simulations. The data for steam are deduced from empirical adjustments of the classical nucleation theory developed by various authors to reproduce pressure and optical data for condensing steam flows in converging-diverging nozzles and turbine stages. By combining the data for nucleation in carrier gases and the data for steam nucleation, an unprecedented temperature range of 250 K is available to study the temperature dependence of nucleation rate. Original results of molecular dynamic simulations for TIP4P/2005 force field in the NVE (system constrained by number of particles, volume and energy) conditions are provided. Correction of classical nucleation theory for non-isothermal nucleation conditions is applied to experimental and simulated data. The nucleation rate data for steam follow a similar temperature trend as the nucleation rate data for water vapour in carrier gases at lower temperatures. The ratio of observed nucleation rates to classical nucleation theory predictions decreases more steeply with temperature than the empirical correlation by Wölk et al. ( J Chem Phys 2002; 117: 4954–4960). On the contrary to experimental data, the ratios of nucleation rates computed from molecular simulations to classical nucleation theory predictions do not show a significant temperature trend.

Solvation of Perfluorsulfonate Ion Exchange Membrane in Non-Aqueous Solvents

As a typical single ion conductor, the perfluorsulfonate (PFSA) ion exchange membrane performance predominantly relies on the interactions amongst cation, sulfonate group and solvent. Such solvation information is crucial to the performance of electrochemical devices. The well-studied interaction between water and proton exchange membranes paved the way for the development of fuel cells and redox flow batteries (1–3). The emerging non-aqueous redox flow battery (NARFB) features alkyl or organic cations. Given the overall inferior performance of NARFBs to aqueous systems, it is important to try to find paths to improve the conductance of the membrane. Despite this and its importance in determining conductivity, the understanding of PFSA cation solvation in non-aqueous solvent is limited so far. We previously reported the surprisingly high ionic conductivity of bulky tetraalkylammonium cations in organic solvents compared to conventional alkyl cations(4). To further investigate the fundamental aspects of cation solvation, we applied different characterization techniques to build connections between ionic conductivity and cation-solvent interaction. Ion mobility data will be discussed in light of solvent uptake. As an example, Figure. 1 shows the relationship between the degree of solvation and relative quantity of deuterated acetonitrile solvating tetrabutylammonium (TBA) form 825EW 3M PFSA. The degree of solvation was derived from solvation signal picked up from carbon-13 NMR on cyanide carbon of deuterated acetonitrile. The degree of solvation increased accordingly with the amount of solvent until it reaches saturation when excess solvent molecules would not participate in the solvation. The respective diffusion coefficients from NMR pulsed gradient diffusion experiments on cations were also presented. A clear signal corresponding to solvent molecules involved in solvation is captured by FTIR and this will also be analyzed as a function of composition and ion type. Acknowledgement We gratefully acknowledge the support of this work by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability (Dr. Imre Gyuk). We also thank 3M for providing membranes. References Vishnyakov A, Neimark AV. Molecular Simulation Study of Nafion Membrane Solvation in Water and Methanol. J Phys Chem B. 2000;104(18):4471–8.Bontha JR, Pintauro PN. Water orientation and ion solvation effects during multicomponent salt partitioning in a Nafion cation exchange membrane. Chem Eng Sci. 1994;49(23):3835–51.Zawodzinski TA, Derouin C, Radzinski S, Sherman RJ, Smith VT, Springer TE, et al. Water Uptake by and Transport Through Nafion® 117 Membranes. J Electrochem Soc. 1993;140(4):1041–7.Lou K, Peng J, Tang Z, Fujimoto C, Zawodzinski TA. Investigation of Ionic Conductivity, Uptake and Cation Diffusion of Perfluorsulfonate and Sulfonated Block Copolymer Ion Exchange Membrane in Non-Aqueous Solvents. Meet Abstr. 2017;MA2017-01(2):166–166. Figure 1. Degree of solvated CN vs relative acetonitrile quantity of TBA+ form 825EW 3M membrane in deuterated Acetonitrile. Figure 1

Redox Flow Battery Electrolyte Design Formulations: Molecular Screening and Engineering

Redox flow battery (RFB) offers great promise to provide transformational progress for large-scale energy storage technology. As the energy-bearing redox active species are dissolved and externally stored in liquid electrolytes, their physiochemical properties dictate the energy density, specific capacity, and cycle life thereby become a single most critical component of RFB. For instance, the concentration and chemical stability of redox active species within the electrolyte will determine the system-specific energy density and temperature window for the RFB operation, respectively1. With the growing interest in developing sustainable RFB systems, there is a pressing task to identify the optimal electrolyte. This led to an active search for an ideal electrolyte which can hold a higher concentration of redox active species with wide chemical and thermal stability. Most electrolyte research has been focused on the empirical study of the effects of the pH, additives and solvent composition2. Using combined spectroscopic and computational studies we established an electrolyte design formulation based on molecular solvate structure tuning3, 4. This helps us to optimize the solubility and redox potential of redox molecule, exemplifying a generic electrolyte design strategy for RFB (see Figure 1). In this presentation, we will discuss the virtual screening and electrolyte design procedures for selecting functional moieties, additive salt and co-solvent to enhances the much-needed redox molecule solubility and stability. References M. Vijayakumar, W. Wang, Z. Nie, V. Sprenkle and J. Hu, Journal of Power Sources 241, 173-177 (2013).M. Vijayakumar, Z. Nie, E. Walter, J. Hu, J. Liu, V. Sprenkle and W. Wang, ChemPlusChem 80 (2), 428-437 (2015).K. S. Han, N. N. Rajput, M. Vijayakumar, X. L. Wei, W. Wang, J. Z. Hu, K. A. Persson and K. T. Mueller, J Phys Chem C 120 (49), 27834-27839 (2016).L. Li, S. Kim, W. Wang, M. Vijayakumar, Z. Nie, B. Chen, J. Zhang, G. Xia, J. Hu, G. Graff, J. Liu and Z. Yang, Advanced Energy Materials 1 (3), 394-400 (2011). Figure 1

Transport & Charge Transfer Near Electrochemical Interfaces: A Quasi-Fermi Perspective

Theories describing the electrochemical double layer have long presented challenges to researchers, yet remain important understanding electrochemical processes. Many of these challenges stem from the multiscale nature of electrochemical interfaces where excess carrier concentrations, whether ions in electrolytes or electrons/holes in semiconductors, can extend 10s of nanometers into the bulk. It is expensive and difficult to capture the full interface with atomistic methods whereas continuum-level mean field approaches often face issues with adequately capturing steric and other physiochemical aspects of the carriers. In both cases, there are issues with the definition of potentials which are experimentally relevant and self-consistent with the associated effects on the participating media [1]. Nevertheless, numerous physiochemical effects that include but are not limited to specific adsorption, dielectric decrement, specific adsorption, osmotic pressures, solvent mixing, and ionic correlations have been identified and described [1-3]. And corrections to mean field theories, such as through the perturbation for finite sized ions, have been put forth to improve predictability [4-6]. In this talk, a quasi-Fermi perspective on transport and space charge near interfaces will be presented. The approach put forward simplifies analysis for electrolytic solutions including for transport at dissimilar interfaces. A perspective on the potential scale and ties to absolute electrode potentials will be presented. The approach will be demonstrated with bipolar membrane electrolyte and photoelectrochemical conversion interfaces. References [1.] A. Baskin and D. Prendergast, Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces, J Electrochem Soc 164 (2017), E3438-E3447. [2.] D. Ben-Yaakov, D. Andelman, D. Harries and R. Podgornik, Beyond standard Poisson-Boltzmann theory: ion-specific interactions in aqueous solutions, J Phys-Condens Mat 21 (2009). [3.] D. Ben-Yaakov, D. Andelman and R. Podgornik, Dielectric decrement as a source of ion-specific effects, J Chem Phys 134 (2011). [4.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. II. Modified Poisson-Nernst-Planck equations, Phys Rev E 75 (2007). [5.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. I. Double-layer charging, Phys Rev E 75 (2007). [6.] M. Z. Bazant, Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics, Accounts Chem Res 46 (2013), 1144-1160.

Transition Metal-Based Catalysts on Stable and Corrosion-Resistant Supports for Oxygen Reduction Reaction

The current proton exchange fuel cells (PEFC) employ platinum group metal (PGM) catalysts in their electrode for oxygen reduction reaction (ORR). However, the excessive cost of PGM catalysts is a major hurdle for realizing the potential of PEFCs, thus necessitating the development of inexpensive non-PGM catalysts. Amongst the different PGM-free catalysts, a complex mixture of carbon (C), nitrogen (N), and transition metals (M) forming M-N-C clusters (M=Co, Fe, Ni, Mn, etc.) are cuurently the leading candidates due to their comparable activity to PGM catalysts and cost-effectiveness [1]. This complex is generally synthesized by the pyrolysis of carbon-based support with metal and nitrogen precursors [2]; however, the carbon-based support suffers from catastrophic failure during repeated start-up/shut-down events wherein the high cathode interfacial potential results in the irreversible corrosion of carbon and hence to the loss of active centers [3]. More distressingly, the reactions typically yield a complex structure, where the active site and reaction mechanism is still under the debate. To overcome this issue, we have investigated the stability and catalytic activity of M-N-C clusters on corrosion-resistive supports, using a combination of theoretical and experimental methods. We have identified conductive and corrosion-resistive binary metal carbides by surveying the Materials Project [4] and Open Quantum Materials Databases [5]. For selected support materials, we have identified the atomic configuration of the M-N-C active sites and investigated the reaction mechanism using density-functional theory (DFT) calculations. We find M-N4 clusters to be energetically preferable on the rocksalt-type carbide supports. The bond distance and electronic structure of the active site are highly dependent on the choice of transition metals of the complex and supports. This dependency affects the adsorption energetics of the reaction intermediates and also plays a determining role on the reaction pathway and overall catalytic activity. Based on this understanding, we have synthesized M-N-C clusters on the most promising carbide supports and measured their activity and corrosion resistivity. Overall, our results demonstrate the rapid discovery of catalysts using a synergistic combination of predictive theory and experiments. Wu, G., Current challenge and perspective of PGM-free cathode catalysts for PEM fuel cells. Frontiers in Energy, 2017. 11(3): p. 286-298.Kramm, U.I., et al., Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells. Phys Chem Chem Phys, 2012. 14(33): p. 11673-88.Castanheira, L., et al., Carbon Corrosion in Proton-Exchange Membrane Fuel Cells: Effect of the Carbon Structure, the Degradation Protocol, and the Gas Atmosphere. ACS Catalysis, 2015. 5(4): p. 2184-2194.Ong, S.P., et al., The Materials Application Programming Interface (API): A simple, flexible and efficient API for materials data based on REpresentational State Transfer (REST) principles. Computational Materials Science, 2015. 97: p. 209-215.Saal, J.E., et al., Materials Design and Discovery with High-Throughput Density Functional Theory: The Open Quantum Materials Database (OQMD). JOM, 2013. 65(11): p. 1501-1509.

Calculation of excess free energy of molecular solids comprised of flexible molecules using Einstein molecule method

Knowledge of free energies of crystalline solid phases is pivotal in determination of phase equilibria; however, their computations using molecular simulations are quite challenging. In this paper, we apply the Einstein molecule method to compute the excess free energies of crystalline molecular solids comprising of molecules described by flexible models. This work can be viewed as an extension of the method described in Aragones et al. [J Chem Phys. 2013;139:a034104]. In this article, we present our calculations of the free energies of ice-Ih described by q-TIP4P/F model and Orcinol Form I described by the OPLS-AA forcefield. The free energies computed for ice-Ih are in agreement with previous reported results, and those of Orcinol are shown to be thermodynamically consistent. We demonstrate that the efficiency of our calculations compares favourably with existing methods. The method described here can be easily implemented in popular publicly available molecular dynamics packages without any modification to their existing source codes.

Theoretical spectroscopy of a NIR-absorbing benziphthalocyanine dye

Benziphthalocyanines are (Yanai et al. in Chem Phys Lett 393:51–57, 2004) phthalocyanines in which one isoindoline unit has been replaced by a phenyl ring. In this study, we focus on a macrocycle of this family recently synthesized by Uchiyama and co-workers (Toriumi et al. Angew Chem Int Ed 53:7814–7818, 2014), and composed of three indoline units (substituted with 2,6-diisopropylphenyl-oxy groups) and one resorcinol unit. We aim at characterizing the possible tautomers to evaluate whether this compound might exist as a mixture of several forms or not. To reach our goals, we use state-of-the-art ab initio theories, i.e., Time-Dependent Density Functional Theory coupled with a refined solvation model (the Polarizable Continuum Model) as well as post-Hartree Fock approaches. We first investigate the stability, the structure and the aromaticity of the possible tautomers before analyzing their spectroscopic signatures. Using an approach going beyond the vertical approximation, we compare experimental and theoretical 0–0 energies and band shapes. This study allows us to point out the dominant presence of the quinoidal form as well as to unravel the vibronic contributions responsible for the specific shape of the optical spectrum.

Electronic Couplings in (Bio-) Chemical Processes.

During the last two decades, 2D optical techniques have been extended to the visible range, targeting electronic transitions. Since the report of the very first 2D electronic measurement (Hybl et al. in J Chem Phys 115:6606-6622, [2001]), two-dimensional electronic spectroscopy (2DES) has allowed fundamentally new insights into the structure and dynamics of condensed-phase systems (Ginsberg et al. in Acc Chem Res 42:1352-1363, 2009; Jonas in Annu Rev Phys Chem 54:425-463, 2003), producing experiments that measure correlations among electronic states of an absorbing species within complex systems. 2DES is used to investigate photo-physical phenomena involving electronic or vibrational couplings in multi-chromophoric systems [energy transfer in photosynthesis is one great example of how 2DES can disentangle various energy transfer pathways (Brixner et al. in Nature 625-628, 2005; Engel et al. in Nature 446:782-786, 2007; Collini et al. in Nature 463:644-647, 2010)], but also ultrafast photochemical processes in which the tracked molecules change permanently or are heterogeneous (Ruetzel et al. in Proc Natl Acad Sci 111:4764-4769, 2014; Consani et al. in Science 339:1586-1589, 2013). We divide this chapter according to some of the major areas that have been established thanks to 2DES in the following fields: heterogeneity of systems, excitation energy transfer mechanisms, photo-induced coherent oscillations associated with electronic and vibrational couplings, and complex chemical reactions (Fig.1). Fig.1 Main fields impacted by two-dimensional electronic spectroscopy (2DES) in condensed phase. The major discoveries of each field will be described in different paragraphs.

Discrete dissociation model of photogenerated inter-chain charge transfer states in external electric field

A new theoretical model of photogeneration yield of free charge carriers on the electric field in π-conjugated polymers was introduced. It generalizes the model of Arkhipov et al. (Chem Phys Lett 372:886–892, 2003a) where the dissociation of the inter-chain charge transfer states is controlled by a thermally activated transition from the lowest quantum state over a potential barrier. Contrary to the previous model based on the effective mass approximation, the new model determines the potential and transfer integrals between HOMO orbitals, using quantum chemical methods. The model successfully explained experimental dependences of photogenerated charge yield in poly{1-[4-(trimethylsilyl)phenyl]-2-phenylacetylene} exhibiting a strong sensitivity on electric field strength over a very large interval. This indicates the model applicability for estimation of fill factor in solar cells. The model was found stable toward various distributions of charge transfer states (on-chain delocalization, charge transfer to side groups, helix structure, etc.) and tunneling effects behind potential barrier.

Correction to: Ab Initio Calculated Results Require New Formulations for Properties in the Limit of Zero Density: The Viscosity of Methane ( $$\hbox {CH}_4$$ CH 4 )

A wide-ranging formulation for the viscosity of methane in the limit of zero density is presented. Using ab initio calculated data of Hellmann et al. (J Chem Phys 129, 064302, 2008) from 80 K to 1500 K, the functional form was developed by guided symbolic regression with the constraints of correct extrapolation to $$T \rightarrow 0$$ and in the high-temperature limit. The formulation was adjusted to the recalibrated experimental data of May et al. (Int J Thermophys 28, 1085–1110, 2007) so that these are represented within their estimated expanded uncertainty of 0.053 % ( $$k = 2$$ ) in their temperature range from 210.756 K to 391.551 K. Based on comparisons with original data and recalibrated viscosity ratio measurements, the expanded uncertainty of the new correlation is estimated outside this temperature range to be 0.2 % to 700 K, 0.5 % to 1100 K, 1 % to 1500 K, and physically correct at higher temperatures. At temperatures below 210 K, the new correlation agrees with recalibrated experimental data within 0.3 % down to 150 K. Hellmann et al. estimated the expanded uncertainty of their calculated data at 1 % to 80 K. The new formulation extrapolates without a singularity to $$T\rightarrow 0$$ .

Correction to: Characterization of fibril dynamics on three timescales by solid-state NMR.

In our recent publication (Smith et al., J Biomol NMR 65:171-191, 2016) on the dynamics of HET-s(218-289), we reported on page 176, that calculation of solid-state NMR R1ρ rate constants using analytical equations based on Redfield theory (Kurbanov et al., J Chem Phys 135:184104:184101-184109, 2011) failed when the correlation time of motion becomes too long.

Capacitive hysteresis at the 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate-polycrystalline gold interface.

We report potential-dependent capacitance curves over a 2-V potential range for the 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate (Emim FAP)-polycrystalline gold interface, and examine the effect of potential scan direction on results. We find very small levels of capacitive hysteresis in the Emim FAP-polycrystalline Au electrochemical system, where capacitance curves show minor dependence on the potential scan direction employed. This is a considerably different response than that reported for the Emim FAP-Au(111) interface where significant hysteresis is observed based on the potential scan direction (Drüschler et al. in J Phys Chem C 115 (14):6802-6808, 2011). Hysteresis effects have previously been suggested to be a general feature of an ionic liquid (IL) at electrified interfaces due to slow interfacial processes and has been demonstrated for numerous electrochemical systems. We provide new evidence that the experimental procedure used to acquire capacitance data and data workup could also have implications on capacitance-potential relationships in ILs. This work serves to progress our understanding of the nature of capacitive hysteresis at the IL-electrode interface. Graphical abstract Subtle changes in experimental methods can lead to significantly different capacitance measurements in ionic liquids. Which is the best approach?